An effective method to solve ODE in terms of power series with regular singular point

The goal of this post is to see if what I did is correct for an exercice but also to show an effective method to use when you need to find power series of an ODE with regular singular point. The method is probably well known but I think that having a detailed example of it can help other students.

: Find around the origin, the solutions in power series the following equation.

:

: Find the singular points

The only x such that is . Therefore, is the only singular point and all other real points are ordinary points.

: Determine if the singular points are regular or irregular

which exists.

which exists.

Therefore, is a regular singular point.

Because is a regular point, this means that and have infinite limits when and are analytics in . Therefore, they have a converging power series expansion of the form:

in a neighbourhoud \ around the origin, where

In this example, and which means that and

: : Find the roots of .

Here, we have . Therefore, and .

: Find the for the first root and the second root.

We first have to compute for some n (let say five), and for . We are going to do the same thing for .

For :

For :

: Find the coefficients for the first root and the second root.

The recurrence relation is given by

and

For

For

: Write the solutions

The solutions are given by:

and

And that's all! Did I made a mistake somewhere? Can I find a better solution than that?

Regards,
Fractalus

Last edited by Fractalus; July 19th 2011 at 04:37 PM.
Reason: typing mistakes